1. Field of the Invention
The present invention relates to a printed circuit board on which a lead-type electronic part having a plurality of leads is mounted by soldering using a nozzle-type solder bath.
2. Related Arts
In general, since a printed circuit board is increasingly required to accommodate parts in high density thereon, lead-type electronic parts with narrow pitches or the like are required to be mounted on a board. On the other hand, practical application of lead-free solder considering environmental problems is an urgent necessity. However, the lead-free solder is inferior in solderability in comparison with leaded eutectic solder which has been used in the related art, and hence short circuit at soldered portions between lead terminals of the lead-type electronic part or the like has been occurred.
In the related art, in the printed circuit board of this type, such a method has been taken in order to prevent generation of solder bridges that adjacent soldering lands are differentiated in size or shape so as to impair balance of surface tension applied on the solder and cause either one of the soldering lands to absorb the solder. (for example, see Patent Document 1).
Also, another method, in which surface areas of outermost soldering land portions are made larger than others to cause the soldering lands having the larger surface areas on both outer sides to absorb excessive solder has been taken (for example, see Patent Document 2).
Alternatively, a method, in which a flat circular vacant land is provided on a rear side of a soldering land for the lead-type electronic part so as to cause the vacant land to absorb the excessive solder, has been taken (for example, see Patent Document 3).
[Patent Document 1] Japanese Unexamined Patent Application Publication No. 62-243393 (pp. 1 to pp. 2, FIG. 3 to FIG. 4)
[Patent Document 2] Japanese unexamined Patent Application Publication No.63-157492 (pp. 2 to pp. 3, FIG. 1 and FIG. 2).
[Patent Document 3] Japanese Unexamined Patent Application Publication No.01-300588 (pp. 4, FIG. 6)
[Disclosure of the Invention]
[Problems to be Solved by the Invention]
The lead-type electronic-part-mounted printed circuit boards in the related art as described above require precise control of a manufacturing process in order to maintain a stable and high-quality soldering which does not cause solder bridges or solder chips between the leads of the lead-type electronic parts. However, the narrower the pitch of the leads becomes, the more defects of soldering tends to occur when the lead-free solder with low solderability is used, and hence it is difficult to maintain a good accuracy.